In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message in a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 10, the radio network controller RNC Integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has also been a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 11(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 11(b), or, as shown in FIG. 11(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 11.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
With reference to FIG. 12, descriptions will be given for a transmission power control in the enhanced uplink. To simplify the description, parts unnecessary for the description, such as an RF section and an antenna, are omitted in the example of FIG. 12.
Firstly, “inner-loop transmission power control” in the enhanced uplink will be described.
In step S101, a transmitter of a mobile station UE transmits data to a radio base station Node B via an uplink.
Here, the transmitter of the mobile station UE periodically transmits a dedicated physical control channel (DPCCH) to which layer 1 control information such as a pilot and a TPC command are mapped. Further, in accordance with presence or absence of data, presence or absence of a transmission allocation, or the like, the transmitter of the mobile station UE transmits either a dedicated physical data channel (DPDCH) or an enhanced dedicated physical data channel (E-DPDCH), to which user data or control information of layer 2 or higher are mapped.
In step S102, an SIR calculating section of a radio base station Node B calculates a signal-to-interference ratio (a reception SIR) of the received DPCCH, and compares a set target SIR with the calculated reception SIR.
In step S103, when the comparison result shows “received SIR>target SIR”, the SIR calculator notifies the transmitter to transmit a “Down” command. On the other hand, when the comparison result shows “received SIR<target SIR”, the SIR calculator notifies the transmitter to transmit an “Up” command. A series of operation described above is referred to as an “inner-loop transmission power control.”
Secondly, “outer loop transmission power control” in the enhanced uplink will be described.
In step S201, a receiver of a radio network controller RNC measures a reception quality of the E-DPDCH (or of the DPDCH).
In step S202, a controller of the radio network controller RNC sets a target SIR in accordance with the measurement result, and notifies the set target SIR to the radio base station Node B. In addition, the controller of the radio network controller RNC determines an amplitude ratio between the E-DPDCH and the DPCCH (hereinafter referred to as “gain factor”) in accordance with the measurement result so as to notify the determined amplitude ratio to the mobile station UE. Here, both of the E-DPDCH and the DPCCH are transmitted from the mobile station UE. A series of operation is referred to as an “outer loop transmission power control.”
The outer loop transmission power control can be adapted to various fluctuation in the radio environment, such as when a mobile station UE shifts to a soft handover state, when a moving speed of the mobile station UE changes, when radio waves are interrupted by a building, or the like.
Furthermore, an “enhanced dedicated physical channel (E-DPCH),” which is a physical channel of an enhanced dedicated channel (EDCH),” is configured of the “E-DPDCH”, to which user data are mapped, and an “enhanced dedicated physical control channel (E-DPCCH),” to which format information required for decoding the E-DPDCH and HARQ related information are mapped.
Here, when the radio network controller RNC fails in decoding the E-DPCCH, the radio network controller RNC is unable to perform a soft combining of the E-DPDCH. Therefore, deterioration in the throughput arises.
Hence, it is known that, in the conventional Enhanced Uplink, it is required to set a to some extent large transmission power offset for the E-DPCCH to the DPCCH (hereinafter, referred to as a transmission power offset) in order to make an error rate of the E-DPCCH equal to or less than a predetermined value.
However, the correlation between the transmission power offset and the error rate of the E-DPCCH is not fixed.
Specifically, the correlation between the transmission power offset and the error rate of the E-DPCCH varies depending on whether or not the mobile station UE is in a soft handover state (SHO state).
Moreover, when the mobile station UE is in the SHO state, the correlation between the transmission power offset and the error rate of the E-DPCCH varies depending on such as the difference in a propagation loss among each of radio links, and the like.
FIG. 13 shows an example of the correlation between the transmission power offset and the error rate of the E-DPCCH, for each of the cases where the mobile station UE is in the SHO state and where the mobile station UE is not in the SHO state.
As described above, the radio network controller RNC is required to set a suitable transmission power offset depending on a situation, and to notify the set offset to the mobile station UE. However, there has been a problem that the radio network controller RNC cannot measure the error rate of the E-DPCCH.    Non-patent Document 1: 3GPP TSG-RAN R1-05363